The street names in Sherwood Forest, a subdivision outside Alexandria, Louisiana, are from the legend of Robin Hood. But the story that played out nearly 10 years ago in one of the homes on Friar Tuck Lane is more like a tale from the Brothers Grimm.

Amanda Kelley had three children: Sadii, 10; Luke, 6; and Jessica, 3. On a winter's day in 2001, she left them briefly to run an errand.

She said that she had left them alone before, "but not for long." This time, she said, she was gone about 15 to 20 minutes.

"Flames around my bedroom window," she told ABC News. "I ran into the house, I felt my way down the hall, it was so black -- you couldn't see a hand in front of your face. ... [I] tried to get up the stairs, to where they should've been to get dressed -- that's where their rooms were and I couldn't make it up the stairs."

"For the first few weeks after they died, I wore it around my neck, and I just would rub it," Kelley said. "And I had someone tell me it was unhealthy and I needed to take it off, [that] it smells like smoke."

But the smoke at the scene of the fire hadn't even cleared when detective Bobby Sandoval of the Rapides Parish Sheriff's Department smelled a crime. In an interview with ABC News, Sandoval said he had suspicions "within the first five minutes."

'Spalling' of Concrete Seen as Evidence of Arson

Sandoval's suspicion was initially based, he said, on Kelley's behavior the afternoon of the fire.

"When I talked to her, I didn't see any emotions as far as crying or anything like that," he said. "She didn't have no burns, she didn't have nothing. ... I mean she just didn't have any signs of any person you would think that went into a boiling black smoke house like she claimed."

But an arson charge requires more than curious behavior; fire investigators want proof. And in this case they claimed to have found it.

After the fire was out, investigators examined the charred cement slab upon which the house had stood. It was pockmarked and pitted. The effect is called "spalling," and investigators believed it was a sign that an accelerant such as gasoline has been used to start the fire.

There was further apparent evidence of arson.

"They tested the soil," said Sandoval. "It tested positive for gasoline, and there was no reason for that gasoline to be there. ... Now we have a crime."

The authorities accused Kelley of burning her children alive. The crime -- arson murder -- can carry a death sentence.

"There's nothing more horrific than that," said Sandoval.

For nine hours in an interview just days after the fire, Sandoval pressed Kelley for a confession, as her father sat beside her. An audio tape of the interrogation captures Sandoval asserting that the children had been murdered.

"My babies were not murdered, Daddy," Kelley replies in the tape. "I did not do this, Daddy ... I did not do this, OK? This is insanity. I don't understand. ... May God put me in hell for eternity if I burned those babies. I didn't do it, Daddy. I didn't."

But the interrogation turned even darker. Sandoval accused Kelley of dousing her children in gasoline.

"You know, the state's Fire Marshal's Office told me that there was gas poured everywhere out there," Sandoval later told ABC. He admitted, however, that the fire marshal had not told him that gas was poured on the kids.

"Sometimes you've got to do what it takes to get to the truth," he said.

Arson: 'Can I Please Go Take the Polygraph?'

But the truth might very well have been destroyed, because on the day after the fire, investigators had the house bulldozed.

"That wasn't my doing," said Sandoval. "That was the state fire marshal's call. I know now that wasn't the right way to handle it."

Meanwhile, as the audio of the interrogation reveals, Kelley kept insisting that she was innocent, even begging to take a lie detector test.

"Can I please go take the polygraph?" Kelley says. "You human beings don't believe ... this could show that at least I'm telling the truth."

But officials never gave Kelley the test. Instead, the case went forward, based on the notion of spalling.

We asked Amanda Kelley if she started the fire.

"No," she said. "Absolutely not. I've stood by my innocence from day one. ... I knew that I was in the presence of a bunch of people wanting to be Horatio on "CSI," and they were really a Barney Fife ... seriously."

Arson: Testing the Spalling Theory

ABC News explored how spalling works at Combustion Science and Engineering, Inc., a lab in Columbia, Md., that specializes in the chemistry and physics of fire behavior.

Doug Carpenter, vice president and principal engineer at the lab, showed us concrete with spalling. It was rough and pockmarked.

Then he showed us what happens when gasoline is actually poured on concrete and set alight.

"One of the things you can see is, you can see the liquid boiling," said Carpenter. "The temperature will never get any higher than the boiling point of that liquid underneath it. So the liquid actually acts to protect the concrete."

Instead of producing spalling, the exact opposite happened. The gasoline-fed fire left the slab charred but completely smooth.

"You can clearly see that flammable liquids alone will not produce spalling of concrete," Carpenter said.

We asked John Lentini, one of the nation's leading fire experts, why more fire investigators weren't current on the science of fires.

"It's not a culture that you learn stuff this way," Lentini said. "You learn from your daddy, who learned from his daddy. The belief system of your mentor is just handed down."

In Kelley's case, those dominoes of outdated beliefs kept falling, right into the hands of the district attorney's office. A Louisiana district court would eventually call the spalling evidence an "old wives' tale."

But for Kelley, vindication was still a long way off.

Rumors Abound in Arson Case

The Kelley story generated a tidal wave of accusations. From the start, almost every day brought another newspaper story and another rumor: Amanda never tried to save her children. The kids were found bound and doused with gasoline.

Meanwhile, Kelley sat in the Alexandria jail, awaiting trial on charges that could carry the death penalty. Mike Small, one of Louisiana's most well-known defense lawyers, took on her case.

Small said the atmosphere surrounding the case was poisonous.

"There is no credible evidence that she set the fire," Small told ABC. "None. ... Defending Amanda was almost like defending Satan."

Still, all the rumors and gossip would mean nothing if there hadn't been evidence that Kelley had set the fire. That evidence started with spalling, but later the case would hinge on prosecution expert John DeHaan, Ph.D., who argued that the fire "was deliberately started in at least two, if not three places."

DeHaan thought the "rapid spread of the fire" signaled that either an "accelerant" was used or "multiple fires" had been started. Either way, DeHaan believed, it was arson.

"It was deliberately started," DeHaan told ABC he concluded at the time. "It was not an accidental fire."

But Lentini sharply disagreed.

"That's just wrong," he said. "It's the most egregious misstatement of science that I've seen in my 30-something years of doing this."

Two nationally-recognized fire experts were drawing two dramatically different conclusions about what happened at Kelley's house.

"There's a huge element of interpretation," said Lentini. "It's all about interpretation. In fact all of forensic science is about interpreting circumstantial evidence... [A] jury can't understand what it means, which is why you need an expert to interpret that evidence for the jury."

Defense attorney Mike Small said the evidence against Amanda Kelley was thin for a capital murder trial.

"In many death penalty cases, the evidence of guilt is overwhelming," Small said. "Amanda turns that model on its head."

For four years, between her indictment and her release on bail, Kelley remained imprisoned on the fifth floor of the Alexandria jail.

Arson: New Prosecutor Reviews Case

Finally, with the original charges thrown out on a procedural issue, prosecutor Mike Shannon took over the case in 2008. Considering possibly starting a new round of arson and murder charges, he decided to review all the evidence, including DeHaan's arson conclusion.

Shannon called DeHaan.

"He said, 'Well, you know I've done other tests. And I can't really go with my original conclusion,'" said Shannon.

"I said... 'What?'"

DeHaan now says that, based on new science and a review of the testimony, he can no longer claim with "scientific certainty" that Kelley's fire was intentionally set.

"He in effect says, 'Everything I said earlier about this fire being intentionally set ... disregard, because it cannot be scientifically supported,'" Small said. "He's essentially saying what our experts had been saying from day one."

Arson: 'Thank God We Didn't Get to That Point'

We asked DeHaan why, when he made the decision that his original conclusion of arson fire might be wrong, he didn't call the prosecutor in the Kelley case.

"Well, because I was unaware of what was going on, this case had been under judicial review for years," DeHaan said. "I respond to the requests of my clients. I don't just invent reasons to go off and create new materials...."

We asked DeHaan if he didn't think that a death penalty case required maybe a higher degree of vigilance on his part.

"All cases deserve my vigilance," he said.

We noted that, had Kelley's case gone to trial, she could have been executed on bad science.

"That is possible, yes," DeHaan said.

Shannon, the prosecutor, said a death sentence in the Kelley case based on bad science had been "certainly a possibility."

"And do you want me to say at this point that had that happened, based on what I know right now -- would've been a miscarriage of justice? Yes," said Shannon. "I would think I believe it would've been... thank God we didn't get to that point."

Still, the point Kelley did get to was tragically bleak: four years in jail, and eight years under the shadow of prosecution.

We asked DeHaan if he had ever called Kelley to explain or apologize in any way. "No," he said. "My responsibility is to my client and the justice system. ... I've been dealing with clients of all kinds for 40 years and I'm sure the experience in unpleasant."

Though the experts and the lawyers now agree there's no proof of arson in the Kelley case, Sandoval, who pressed so hard for Kelley's confession for all those years, hasn't moved an inch.

We asked him how it felt when he realized Kelley was not going to be charged with arson.

"I had a nauseating feeling," he said. "Because there's not a doubt in my mind that this lady didn't kill her children."

Kelley declined to respond.

"I wouldn't say anything to him," said Kelley. "I pray for him. He's pitiful. I don't know how he sleeps."

But Kelley's nightmare wasn't over. Shannon decided there was negligence on her part for leaving the kids alone during the time the fire broke out.

He filed new charges in what was then legally considered nothing more than an accidental fire -- charges that could have still potentially put her in prison for life. Small advised Kelley that there was no way to be sure what would happen in a trial.

She finally decided to plead guilty to a lesser charge of negligent homicide with the agreement that she serve no further jail time.

As Kelley left the courthouse, for the first time she was legally clear... but not free. She said she deals with the guilt over what happened every day, and that due to all the years of rumors and false accusations, she can't feel that she got justice.

"With all the lies and rumors and the false accusations, no," said Kelley. "It will one day though. I believe that. I believe we all answer for what we've done when we stand before God, and Sandoval will. He'll have to answer."

Watch 20/20 tonight at 10 p.m. for the conclusion of the Amanda Kelley case.